Collaborative Research: Isothermal Phase Transition in Lipid Vesicles and Swell-Burst Cycles

在这个项目中，PI将使用理论、模拟和实验相结合的方法来研究脂质膜的复杂性。本项目结合高分子物理、膜力学与生物工程、表面与界面科学、软凝聚态物质等领域的概念，研究生物膜的组织结构。建模工作将开发新的和新颖的数学和新的数值格式来解决由此产生的微分方程。目前对多组分巨型单层囊泡（GUVs）如何响应渗透压差的理解尚不完整，实验观察表明，需要一个耦合膜动力学和三维流体流动的非线性模型来充分解释系统的非线性。发展这一理论框架，并提供洞察到潜在的物理是至关重要的膜如何经历形态转变的理解。这些模型将解释现有的实验，并预测膜对不同渗透负荷和膜成分的反应。了解这一过程对于更好地设计体外重构系统（如囊泡和细胞系统）具有重要意义。这项工作本质上是跨学科的，在生物系统中使用数学和物理学。这两个领域都将受益于这种研究生物现象的方法；该理论将以实验为基础，并为设计未来的实验做出预测。这项研究将会整合到pi的教学工作中，以开发工程学和生物学的新课程。在开展研究项目的同时，pi将继续努力提高UC系统的多样性。生物膜本质上是脂质和蛋白质的异质混合物。这种非均质性的一个关键特征是液体有序相和液体无序相并存。这种共存被认为是脂筏形成的关键组织原则。考虑到细胞的复杂性，研究细胞系统中不同相的形成和组织在实验上具有挑战性。具有可控成分的巨大单层囊泡，使我们能够研究双层膜中的脂质行为，并深入了解相行为，这对理解细胞膜非常重要。尽管guv在实验中得到了广泛的应用，但我们对脂质相分离的理论理解仍然很初级，因为现有模型关注的是预先存在的结构域之间的线张力，而不是实验观察到的结构域生长和膨胀破裂周期。本项目的目的是建立多组分guv等温相分离和胀爆循环的定量模型，并对模型预测进行实验验证。研究1：溶质射流动力学。我们将使用理论、模拟和实验来了解控制孔隙半径、囊泡半径和孔隙寿命的因素。渗透压囊泡两相分离的研究。使用多组分脂质膜的粘弹性模型，我们将研究控制能量在畴生长和真正相变中的作用。我们将通过调整渗透压差、脂质组成和样品温度来实验测试模型预测。研究区域形成与井喷旋回之间的3-耦合。在这项研究中，我们将开发数学框架来模拟振荡相分离的完整动力学，以及在初步实验中观察到的膨胀-破裂循环。该模型将结合研究1中概述的孔隙形成动力学，以及研究2中包含膜粘度的区域生长模型。所提出的活动的意义在于，它不仅阐明了脂质混合物的基本性质，降低了维度，双层结构，而且还提供了设计合成原细胞室的设计原则，用于蛋白质的体外生产，限制化学和生物医学相关货物（例如，酶，药物和显像剂）的输送。通过理论、模拟和实验的结合，这项工作将能够深入了解脂质膜的复杂性。拟议活动的长期影响源于这样一个事实，即该项目结合了聚合物物理学、膜力学和生物工程、表面和界面科学以及软凝聚态物质等领域的概念。这里概述的建模工作将导致新的和新颖的数学和新的数值方案来解决所产生的微分方程。

In this project the PI, using a combination of theory, simulations and experiments, will investigate the complexities of lipid membranes. The project combines concepts from the fields of polymer physics, membrane mechanics and bioengineering, surface and interface science, and soft condensed matter to study the organization of biological membranes. The modeling efforts will develop new and novel mathematics and new numerical schemes to solve the resulting differential equations. The current understanding of how multi-component giant unilamellar vesicles (GUVs) respond to osmotic pressure differentials is incomplete, and experimental observations indicate that a non-linear model coupling membrane dynamics with 3D fluid flow is needed to fully explain the non-linearities of the system. Developing this theoretical framework and providing insight into the underlying physics is crucial for the understanding of how membranes undergo morphological transitions. These models will explain existing experiments and also predict membrane response to different osmotic loads and membrane compositions. Understanding this process is important for better experimental design of in vitro reconstituted systems such as vesicles and also cellular systems. The work is inherently interdisciplinary, using mathematics and physics in biological systems. Both fields will benefit from this approach to studying biological phenomena; the theory will be grounded in experiments and also make predictions to design future experiments. This research will be integrated into the teaching efforts of the PIs in developing new courses at the interface of engineering and biology. The PIs will continue their efforts in enhancing diversity in the UC system while pursuing the research program. Biological membranes are inherently heterogeneous mixtures of lipids and proteins. A key characteristic of this heterogeneity is the coexistence of liquid-ordered and liquid-disordered phases. This coexistence is thought to be the key organizing principle for the formation of lipid rafts. Studying the formation and organization of the different phases in cellular system is experimentally challenging, given the complex nature of the cells. Giant unilamellar vesicles with controlled compositions, allow us to study lipid behavior in bilayer membranes and gain insight into phase behavior which is important for understanding cellular membranes. Although GUVs are used widely experimentally, our theoretical understanding of lipid phase separation remains rudimentary, since existing models focus on the line tension between preexisting domains and not on domain growth and swell-burst cycles, which are the features observed experimentally. The objectives of this project are to formulate quantitative models of isothermal phase separation and swell-burst cycle in multi-component GUVs and test model predictions experimentally. STUDY 1-DYNAMICS OF SOLUTE EFFLUX. We will use theory, simulations, and experiments to understand the factors that control pore radius, vesicle radius, and the lifetime of the pore. STUDY 2-PHASE SEPARATION IN OSMOTICALLY STRESSED VESICLES. Using a viscoelastic model of multi-component lipid membranes, we will investigate the role of governing energetics in domain growth versus true phase transitions. We will experimentally test the model predictions by tuning the osmotic pressure difference, lipid composition, and sample temperature. STUDY 3-COUPLING BETWEEN DOMAIN FORMATION AND SWELL-BURST CYCLES. In this study, we will develop the mathematical framework to model the complete dynamics of the oscillatory phase separation coupled with the swell-burst cycle observed in the preliminary experiments. This model will combine the dynamics of pore formation outlined in Study 1, with the domain growth model including membrane viscosity in Study 2. The significance of the proposed activities lies in its promise to not only elucidate the fundamental properties of mixtures of lipids reduced dimensional, bilayer configuration but also furnish design principles for designing synthetic protocellular compartments for applications spanning in vitro production of proteins, chemistry in confinement, and delivery of biomedically relevant cargo (e.g., enzymes, drugs, and imaging agents). Using a combination of theory, simulations and experiments, this work will be able to provide insight into the complexities of lipid membranes. The long-term impact of the proposed activities stems from the fact that the project combines concepts from the fields of polymer physics, membrane mechanics and bioengineering, surface and interface science, and soft condensed matter. The modeling efforts outlined here will result in new and novel mathematics and new numerical schemes to solve the resulting differential equations.